If the anticyclone is indeed back, this day of Wednesday May 8, 2024 remained autumnal between Belgium and Île-de-France. The fault is low clouds that are more tenacious than expected. Explanations.
An autumnal May 8 in the north
If morning gray had been forecast for the north of France, from Belgium to Île-de-France, there was talk that it would dissipate during the day to give way to nice clearings in the afternoon. noon. However, this was not the case. In Hauts-de-France, Haute-Normandie, Île-de-France, Champagne and Yonne, a large part of this day of Wednesday May 8, 2024 took place under gray skies due to ‘a more stubborn grayness than initially expected.
Satellite image of Wednesday May 8, 2024 in the early afternoon – via NASA
Thus, the improvement hoped for on this public holiday of May 8, 2024 did not take place in the north of the territory. In Paris, the gray weather arrived shortly before 7 a.m. and lasted for a good part of the day, bringing an autumnal atmosphere. The entire north of France suffered the same fate. The inhabitants of Hauts-de-France and Île-de-France, who number more than 18 million, experienced a much less pleasant May 8 than expected.
Arrival of gray weather in Paris from 7 a.m. this Wednesday, May 8, 2024 – Paris Weather webcam
In addition to the absence of sunshine, this stubborn grayness considerably slowed down the progression of temperatures during the day. While the 20°C mark should have been reached according to the models, thanks to the return of clearing, the covered sky did not even allow the thermometer to reach that of 15°C. In Hauts-de-France and Île-de-France, temperatures often peaked between 12 and 14°C, levels 4 to 5°C lower than normal. With the clouds and the freshness, the atmosphere was more autumn than spring.
Temperatures measured this Wednesday, May 8, 2024 at 4 p.m. – Weather Paris
Why this forecast error?
Predicting low-level clouds is one of the most difficult and it is not uncommon for models to get it wrong. This was the case for this Wednesday, May 8, 2024. If most scenarios had considered the presence of this grayness in the morning, it should dissipate during the afternoon, except in the far north (notably in Flanders). However, the air remained more humid than expected in the lower levels throughout the day, allowing the gray weather to persist between Belgium and northern Burgundy, including Hauts-de-France and Île-de-France. France.
Comparison of cloudiness for the afternoon of Wednesday May 8, 2024 between the model and reality – via meteociel.fr
The explanation lies in the positioning of the anticyclone. Currently re-inflating over the British Isles, the latter was directing a northern sector flow over the northern regions on May 8. Thus, it was humid air coming from the North Sea which infiltrated the north of France. This humidity – which had been underestimated by the models – maintained the grayness, allowing it to persist for a large part of the day. Moreover, we can clearly see on the satellite image that the area affected by the stubborn grayness is literally the one fed by the humid northern flow, straight as an i between Flanders and the Yonne.
Weather situation in Europe this Wednesday, May 8, 2024 – Weather Cities
The benefit of expert forecasts on Météo Cities
Low clouds are among the most difficult to predict, even at very short notice. This is the whole point of Météo Cities. Our forecasts are checked and constantly re-evaluated by our forecasters, unlike automatic forecasts available on 99% of sites and applications. This allowed us to modify our forecasts this Wednesday morning and announce a much cloudier (and therefore cooler) day than expected for the 12 million inhabitants of Paris and Île-de-France, while the mobile weather apps continued to report sunny and mild weather, dictated by the forecast model.
Comparison of the automatic forecasts of the app on iPhone and our expert forecasts on Météo Paris
Meteorology has never been, is not and probably never will be an exact science, as a tiny grain of sand in the equation can change the situation. Human expertise plays a vital role because only the human eye is able to understand model errors and adapt to them by correcting the situation if necessary.
